A driving assistance system for providing a state of a rear side of a vehicle to the driver by installing backward an equipped camera into a rear portion of a vehicle and displaying an image picked up by the camera on a monitor screen provided near a driver's seat is spreading nowadays. At this time, a parking assistance system having a function of assisting the parking operation of the driver by superposing/displaying various guidance as a clue of the parking operation on the monitor screen appears.
For example, in the parking assistance system set forth in JP-A-2001-180405, a locus line of a particular portion such as a front left corner portion, or the like of driver's own vehicle is superposed/displayed on the monitor screen such that the driver can decide easily whether or not driver's own vehicle comes into contact with the obstacle such as the surrounding vehicle, etc. during the parking operation. FIG. 12 is a view showing an example of a screen construction of the parking assistance system set forth in JP-A-2001-180405 in the related art. The related art will be explained with reference to FIG. 12 hereunder.
In this related art, guides 2, 3 indicating a vehicle width of driver's own vehicle in the straight backing, guides 4, 5 indicating rear ends of the guides 2, 3 respectively, and guides 6, 7 indicating predetermined rear positions inclined leftward and rightward from driver's own vehicle respectively are displayed on a monitor screen 1 that displays the image on the rear side of the vehicle. In addition, in this related art, a steered-amount guide 8 (an inner frame of a double rectangular display in FIG. 12) which moves in response to a steering angle along the guides 6, 7 (the guide 6 in this illustration) is also displayed.
When the driver carries out the parallel parking while monitoring this monitor screen 1, at first the driver backs straight driver's own vehicle in parallel with the road, and then stops own vehicle at a point of time when the guide 6 overlaps with a target point S1 in a target parking space T (an outer frame of the double rectangular display in FIG. 12). Then, the driver turns the steering wheel until a steered-amount guide 41 almost overlaps with the target parking space T on the monitor screen 1 (FIG. 12 shows the state that the steered-amount guide 41 overlaps with the target parking space T). Then, when both overlaps with each other, the driver further backs driver's own vehicle while maintaining the steering angle as it is.
At this time, the parking assistance system displays a locus line 9 of a front left corner portion of driver's own vehicle on the monitor screen 1. Because this locus line 9 is displayed on the monitor screen 1, the driver can see whether or not the front left corner portion of driver's own vehicle is going to interfere with an obstacle (image 10) in the middle of the route to the target parking space T when he or she parks his or her own vehicle in parallel with the left side of the road.
Then, the driver backs driver's own vehicle while holding the steering angle of the steering wheel, and then stops driver's own vehicle when the guide 5 comes up to the position of the target point S1. Then, the driver turns the steering wheel in the opposite direction to its maximum as the steer without driving, and then backs driver's own vehicle. The operations required for the parallel parking are completed when the guide 2 of the vehicle width is positioned in parallel with a side line 11 of the road.
In the case that the parallel parking is carried out by using the above parking assistance system in the related art, the driver can know previously whether or not driver's own vehicle comes into contact with the neighboring vehicle, based on the locus line 9 of the front left corner portion of driver's own vehicle being displayed on the monitor screen.
However, in the parking assistance system of the related art, a sensor for sensing the steering angle, a steering signal receiving portion, a predictive locus computing portion, etc. must be equipped to display the locus line 9 with good precision. Therefore, such a problem existed that a construction cost is increased.
Also, in the parking assistance system of the related art, there existed such a problem that, when the locus line 9 overlaps with the obstacle and driver's own vehicle touches the obstacle if the parking operation is continued as it is, the driver must search the position, at which the locus line 9 does not overlap with the obstacle, every time by correcting the parking operation starting position of driver's own vehicle many times.
In addition, since the image on the rear side of the vehicle displayed on the monitor screen is an image picked up by a wide-angle camera, such image is displayed smaller and distorted larger as the position becomes more distant from the rear side of the vehicle. Therefore, it is difficult to decide with high precision whether or not the guide 6 coincides with the target position S1 shown in FIG. 12. As a result, such a problem existed that it is difficult to park driver's own vehicle on the target parking space T with good precision.
An object of the present invention is to provide a parking assistance system for displaying guidance, which makes it possible for the driver to intuitively decide a possibility of contact of a front left or right corner portion of driver's own vehicle with a surrounding vehicle or an obstacle and exactly decide a steering point of a steering wheel during a parallel parking, on a monitor screen.
Another object of the present invention is to provide a parking assistance system for displaying guidance with high safety, which makes it possible to improve an operability and easily decide a possibility of contact of a front left corner portion (or a front right corner portion) of driver's own vehicle with a surrounding vehicle or an obstacle during a left-side (or right-side) parallel parking by limiting a parking operation to a straight backing operation or a backing operation in the condition that a steering wheel is always turned to its maximum, on a monitor screen.